NAME

       SDBM_File - Tied access to sdbm files

SYNOPSIS

        use Fcntl;   # For O_RDWR, O_CREAT, etc.
        use SDBM_File;

        tie(%h, 'SDBM_File', 'filename', O_RDWR|O_CREAT, 0666)
          or die "Couldn't tie SDBM file 'filename': $!; aborting";

        # Now read and change the hash
        $h{newkey} = newvalue;
        print $h{oldkey};
        ...

        untie %h;

DESCRIPTION

       "SDBM_File" establishes a connection between a Perl hash variable and a file in SDBM_File
       format.  You can manipulate the data in the file just as if it were in a Perl hash, but
       when your program exits, the data will remain in the file, to be used the next time your
       program runs.

   Tie
       Use "SDBM_File" with the Perl built-in "tie" function to establish the connection between
       the variable and the file.

           tie %hash, 'SDBM_File', $basename, $modeflags, $perms;

           tie %hash, 'SDBM_File', $dirfile,  $modeflags, $perms, $pagfilename;

       $basename is the base filename for the database.  The database is two files with ".dir"
       and ".pag" extensions appended to $basename,

           $basename.dir     (or .sdbm_dir on VMS, per DIRFEXT constant)
           $basename.pag

       The two filenames can also be given separately in full as $dirfile and $pagfilename.  This
       suits for two files without ".dir" and ".pag" extensions, perhaps for example two files
       from File::Temp.

       $modeflags can be the following constants from the "Fcntl" module (in the style of the
       open(2) system call),

           O_RDONLY          read-only access
           O_WRONLY          write-only access
           O_RDWR            read and write access

       If you want to create the file if it does not already exist then bitwise-OR ("|")
       "O_CREAT" too.  If you omit "O_CREAT" and the database does not already exist then the
       "tie" call will fail.

           O_CREAT           create database if doesn't already exist

       $perms is the file permissions bits to use if new database files are created.  This
       parameter is mandatory even when not creating a new database.  The permissions will be
       reduced by the user's umask so the usual value here would be 0666, or if some very private
       data then 0600.  (See "umask" in perlfunc.)

EXPORTS

       SDBM_File optionally exports the following constants:

       •   "PAGFEXT" - the extension used for the page file, usually ".pag".

       •   "DIRFEXT" - the extension used for the directory file, ".dir" everywhere but VMS,
           where it is ".sdbm_dir".

       •   "PAIRMAX" - the maximum size of a stored hash entry, including the length of both the
           key and value.

       These constants can also be used with fully qualified names, eg. "SDBM_File::PAGFEXT".

DIAGNOSTICS

       On failure, the "tie" call returns an undefined value and probably sets $! to contain the
       reason the file could not be tied.

   "sdbm store returned -1, errno 22, key "..." at ..."
       This warning is emitted when you try to store a key or a value that is too long.  It means
       that the change was not recorded in the database.  See BUGS AND WARNINGS below.

BUGS AND WARNINGS

       There are a number of limits on the size of the data that you can store in the SDBM file.
       The most important is that the length of a key, plus the length of its associated value,
       may not exceed 1008 bytes.

       See "tie" in perlfunc, perldbmfilter, Fcntl